MARAJÓ ISLAND, Brazil — Legends flourish about how the first Asian water buffaloes made it to this colossal island in the Amazon River Delta.

One tale holds that they originally came from the steamy rice fields of French Indochina, but washed up here after the wreck of a ship bound for French Guiana. Another yarn contends that inmates escaping from a penal colony in French Guiana used the adroitly swimming buffaloes to help guide their makeshift barges all the way to freedom in Marajó’s mangroves.

However they arrived, the invasive species multiplied on Marajó, and now numbers about 450,000 on an island the size of Switzerland. So much of daily life here revolves around the water buffaloes that islanders haul garbage with them, race them during festivals and regularly savor fillets of buffalo steak smothered in cheese made from, yes, buffalo milk.

“The importance of the buffalo in Marajó got us thinking,” said Maj. Francisco Nóbrega, 41, an official with the 8th Battalion of the military police of Pará, the vast state in Brazil’s Amazon that encompasses Marajó. “Why not patrol on buffalo as well?”

Seizing on that idea, one of Brazil’s most unusual policing experiments came into existence. Water buffaloes have been domesticated elsewhere for thousands of years, called “the living tractor of the East” for their role in plowing fields, but officers with the 8th Battalion here hatched a plan to make their rounds atop the crescent-horned beasts.

Once a year, the battalion even places its buffaloes and police officers on a ship to Belém, the capital of Pará, where each Sept. 7 they strut down avenues in parades commemorating Brazil’s declaration of independence from Portugal.

The buffalo unit started in the 1990s, patrolling the sleepy outpost of Soure, which has about 23,000 people, and breaking up the occasional bar fight.

Over the years, the mission has expanded to include pursuing suspects who flee into Marajó’s wilds and cracking down on buffalo rustling on the island’s far-reaching ranches.

“Water buffaloes are remarkable swimmers, better than dogs, and more agile than horses when it comes to moving through mud,” said José Ribamar Marques, an official on Marajó with Embrapa, the pioneering Brazilian research company that focuses on tropical ranching and agriculture. “The animal is also docile, facilitating its contact with human beings.”

Indeed, the buffaloes of Marajó have certain advantages.

Their widely splayed hooves allow them to move with relative ease through muddy swamps. They also seem to deal well with the punishing heat of Marajó, which sits almost directly on the Equator.

Several breeds thrive on Marajó, like the Murrah, prized for its meat and milk, and the Carabao, known for its sickle-shaped horns. (Asian water buffaloes differ from the American buffalo, which is a bison, despite its name.)

And there is another benefit of using water buffaloes in police work, some officials say: It helps lower tensions.

“This is the kind of place where everybody knows everybody’s business,” said Claudio Vitelli, 45, a police officer who regularly patrols on a buffalo. “I’ve had to arrest an uncle of mine for a petty offense, and before that, a cousin.”

“Being the guy on the buffalo makes me more approachable, making my job a little bit easier,” he added.

Brazil’s military police are somewhat akin to state police in the United States, in the sense that they are controlled by state governments. But the forces are imbued with militarized traditions, like wearing combat fatigues, and their heavy-handed policing methods have produced an array of rights abuses, including forced disappearances and killings of people presumed to be innocent.

Despite its laid-back vibe, this island is no stranger to the ire produced by such episodes. After a police officer fatally shot a man in 2011 in São Sebastião da Boa Vista, a town on Marajó, furious residents freed the prisoners in the local jail, burned the police station to the ground and sent police officers fleeing to other parts of the island.

In the town of Soure, where the 8th Battalion operates from a small station adjacent to a corral with about 10 buffaloes, police officers claim that patrolling on the animals can assuage tension with residents by bringing low-ranking personnel in the military police, commonly called soldiers, into contact with people who use buffaloes for transportation, farming or other work.

The policing experiment has drawn interest elsewhere in the country. Piauí, a highbrow magazine in Rio de Janeiro, called the unit Brazil’s “Buffalo Soldiers,” a riff on Bob Marley’s reggae classic and the song’s inspiration, the African-American regiments of the American West in the 19th century. (The American soldiers rode horses, however, not buffaloes.)

Some on Marajó appreciate the attention.

“Few people know how important our buffaloes truly are, but our police are raising awareness,” said Antenor Penante, 30, the manager of a family-owned tannery, who proudly described how his business uses the dried penises of water buffaloes to make horse whips and riding crops.

“We don’t waste any part of the buffalo,” said Mr. Penante, pointing to a collection of purses made from buffalo scrotums in his tannery’s store. “Marajó should be proud of its herds.”

Though water buffaloes can be found elsewhere in Brazil, other police forces seem to have avoided using the animals for policing.

Still, officers in the 8th Battalion say they are prepared to lend their buffalo expertise to interested parties, mentioning the Brazilian Army’s respected Jungle Warfare Instruction Center, which sent instructors here to learn how to use Asian water buffaloes to replace mules and horses for supplying troops in the rain forest.

“Brazil is a tropical country, and that means we have to find tropical solutions for the challenges we face,” said Emerson Cassiano, 42, a police officer in the buffalo unit.

“My friends tease me, saying a buffalo is only good for cutting up into steaks, but that’s an ignorant point of view,” Mr. Cassiano added. “Look what people have accomplished since they started riding horses instead of eating them. Our buffalo patrol could be the start of something huge.”

Lis Horta Moriconi contributed reporting from Rio de Janeiro.

A version of this article appears in print on , on Page A6 of the New York edition with the headline: To Soften Image, Officers Patrol on Horned Beasts. Order Reprints | Today’s Paper | Subscribe

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